In the ready-mixed mortar, the addition amount of hydroxypropyl methyl cellulose HPMC is very low, but it can significantly improve the performance of the wet mortar, which is a major additive that affects the construction performance of the mortar. Cellulose ethers with different viscosity and added amount have a positive effect on the improvement of the performance of dry mortar. At present, many masonry and plastering mortars have poor water retention properties, and water slurry separation occurs after a few minutes of standing still. Water retention is an important performance of methyl cellulose ether, and it is also a performance that many domestic dry mortar manufacturers, especially those in areas with higher temperatures in the south, pay attention to. The factors affecting the water retention effect of dry mortar include the amount of HPMC added, the viscosity of HPMC, the fineness of particles and the temperature of the environment in which it is used.
1. Concept: Cellulose ether is a synthetic high molecular polymer made from natural cellulose through chemical modification. Cellulose ether is a derivative of natural cellulose. The production of cellulose ether is different from synthetic polymers. Its most basic material is cellulose, a natural polymer compound. Due to the special structure of natural cellulose, cellulose itself has no ability to react with etherifying agents. But after the swelling agent is treated, the strong hydrogen bonds between the molecular chains and within the chain are destroyed, and the active release of the hydroxyl group turns into reactive alkali cellulose. After the etherification agent reacts, the -OH group is converted to the -OR group. Obtain cellulose ether. The nature of cellulose ether depends on the type, quantity and distribution of substituents. The classification of cellulose ethers is also based on the types of substituents, the degree of etherification, solubility and related applications. According to the type of substituents on the molecular chain, it can be divided into monoether and mixed ether. The HPMC we usually use is mixed ether. Hydroxypropyl methyl cellulose ether HPMC is a product in which part of the hydroxyl group on the unit is replaced by methoxy group and the other part is replaced by hydroxypropyl group. HPMC is mainly used in building materials, latex coatings, medicine, daily chemistry, etc. Used as a thickener, water-retaining agent, stabilizer, dispersant, and film-forming agent.
2.Water retention of cellulose ether: in the production of building materials, especially dry mortar, cellulose ether plays an irreplaceable role, especially in the production of special mortar (modified mortar), it is indispensable. component. The important role of water-soluble cellulose ether in mortar is mainly in three aspects. One is excellent water retention capacity, the other is the influence on the consistency and thixotropy of mortar, and the third is the interaction with cement. The water retention effect of cellulose ether depends on the water absorption of the base layer, the composition of the mortar, the layer thickness of the mortar, the water demand of the mortar, and the setting time of the coagulating material. The water retention of the cellulose ether itself comes from the solubility and dehydration of the cellulose ether itself.
the thickening and thixotropy of cellulose ether: The second role of cellulose ether-thickening depends on: the degree of polymerization of cellulose ether, solution concentration, temperature and other conditions. The gelation properties of the solution are unique properties of alkyl cellulose and its modified derivatives. Gelation characteristics are related to the degree of substitution, solution concentration and additives.
The good water retention capacity makes the cement hydration more complete, can improve the wet tackiness of the wet mortar, increase the bonding strength of the mortar, and the time can be adjusted. The addition of cellulose ether to mechanical spraying mortar can improve the spraying or pumping performance of the mortar, as well as the structural strength. Therefore, cellulose ether is being widely used as an important additive in ready-mixed mortar.
Post time: Dec-16-2021